


The World Beneath Our Feet

by Life_ontheLine



Category: Slugterra, 僕のヒーローアカデミア | Boku no Hero Academia | My Hero Academia
Genre: F/M, Izuku gets his own Wrist Blaster, Izuku gets taught by Junjie and Eli, Midoriya Izuku Has One for All Quirk, Other Additional Tags to Be Added
Language: English
Status: In-Progress
Published: 2019-10-28
Updated: 2020-07-20
Packaged: 2021-01-05 14:02:09
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence
Chapters: 3
Words: 4,024
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21209735
Author URL: https://archiveofourown.org/users/Life_ontheLine/pseuds/Life_ontheLine
Summary: Izuku, Ochaco, and Kyoka get stuck in the 99 Caverns.Alternatively, MHA x Slugterra.





	1. The 99 Caverns

**Author's Note:**

> im sorry

Izuku Midoriya wakes up to beautiful scenery. But instead of being greeted with a blue sky, he’s met with a far-off mossy ceiling. It’s decorated with flowers and vines of every kind, and some that he hasn’t seen before. 

He gets up, holding his head and looking around him. Mushrooms and dense vegetation surrounded him. The mushrooms and fungi were _ huge! _ They were glowing, and there were sort of mini-trees and the large ones! They had to be a third of U.A.’s height!

He remembers falling down with someone. Who? He glances around near the grass under his feet, seeing a very familiar boot peeking from behind a mushroom stalk. He runs over, taking a look. 

Kyoka Jiro, his classmate, lay there, unconscious, with bruises and scratches all over her body. Broken bones. Probably. She was still breathing, so that was good. Her arm was broken. If only Recovery Girl was here. She could help her with that broken arm.

He looked back up at the ceiling. There was a massive hole. He tried to see and guess if he could jump that far. 

Nothing. Even the 0-Pointer he demolished at the entrance ceremony was only a third of this massive cavern’s size. 

He looked all around him. There were these sort of… bipedal-ish slugs. They didn’t move around on their underbelly, rather their… feet? He kneeled down and offered his hand to one of them. It was small. It had a singular white tooth on the lower ‘jaw’, had a beautiful metallic jade outer skin, and its underbelly was a sort of matte gunmetal gray.

“Hey, little guy.” 

It chirped in response, sniffing his glove. The slug hopped on his hand, and he gently brought it up to neck-height. He smiles and rubs the slug’s head with his thumb carefully. It started to chirp happily. 

It hopped on his shoulder. He chuckles and looks back to Jiro, who began to wake back into consciousness and then groaned painfully. 

“Deku!” 

Uraraka. Where was she? He glanced around, turning completely on his heels. Wait… They got down here with minimal bruising. He looks up, and sure enough, there’s Uraraka, floating in midair. He charges up eight percent of One for All, launching up to grab her. She holds on tightly as they fall, deactivating her Quirk. 

Upon landing, he sets her down. She holds her stomach, running behind a mushroom and vomiting. Izuku could see the sparkles fall out behind the mushroom. 

He turns around to check on Jiro. She’s awake, and just lying there. She takes a deep breath, and lets out a loud sigh. Uraraka approaches from the back, stopping beside him. 

“Deku, where are we?”

“I don’t know, but it’s underground somewhere. We came through that hole.” 

“That doesn’t seem that far up. Maybe you can get us out of here?”

“No. Tried bouncing off the cavern wall and didn’t get far. I could probably use all of my power, but I’d break my bon-” 

He hears an explosion in the hole’s direction. There are burn marks around the hole and it’s covered. It’s been sealed off. 

“Damn it.” 

“It’s been sealed off?! Why!?”

“I don’t know, okay? Calm down, Uraraka!” 

Uraraka started fussing, breaking into a muttering spree. Like him. They weren’t in any real danger, but he just sighs. She quickly stops after a tap on the shoulder from him.

A sort of beam fires, and another explosion is heard. He jumps slightly. Gunfire? Down here? They have _ guns?? _ Out of all three of them, only he was able to barely dodge gunfire. Firing rate was very slow, but they caused explosions. Cannons? They had beam cannons? _ What?? _

He produced a flare and zippo lighter from his left pouch, handing it to Uraraka. 

“Light it if you’re in trouble, I’ll come as soon as possible.”

Uraraka nods in acknowledgement. He gently laid the slug on his shoulder on Uraraka’s shoulder. He activates eight percent of One for All, going for a running jump. He launches into the air, landing near the source of the cannonfire. 

He lands in some sort of forest, and hops up to the top of a tree. There was a throwdown going on between two beings. One was a large blue humanoid creature. Everything about them was human, aside from the blue skin and overly large upper body. The other person was very different. They were… ghoulish, for lack of a better word. They had pale skin and horns that protruded from their head. They had red eyes and black irises, with goat-like legs and claws on every extremity. 

Judging from the demeanor, he could tell that the pale-skinned being was the one oppressing the large blue male. They readied a shot to fire at the blue male and he reacted on instinct. 

Neon green arcs of lightning cloaked his body, empowering him with the might of One for All. He drops down from the tree, pushing against the dirt and launching towards the ghoulish being. He clenches his fist, socking the person clear across the face. The ghoulish being got launched into the tree, effectively knocking them out. 

The large blue male looked at him in awe. Then he spoke.

“Holy crap! How’d you do that!?” 

He looks around, then points to himself in confusion. 

“Me?”

“Yeah, you! That was awesome!” 

“O-Oh, thank you.” 

He was being praised. Didn’t exactly know how to deal with that. 

“I should be getting back to my friends. Oh, before I forget, are there any doctors or hospitals around here? One of them has broken bones.” 

“Gosh. Hmm… There’s always Redhook, but I think he’s a bit senile. Hmm… You could go to the Shane Gang. They got a healer slug that’s the definition of ‘miracle worker’."

“A slug?” 

The large blue male points to the blue canisters on his bandoleer. Inside are the slug-like creatures. They came in a variety, those with antennae and with different vibrant colors, allowing for easy differentiation.

“These lil’ guys are slugs. They protect us and keep the Caverns in balance.” 

“Huh.. Anyways, do you know where the Shane Gang live or are now?”

“Sure I do, their hideout is just there.” 

The large blue man points to a tree, with a sort of oddly shaped house. 

“Thanks, sir!” He activates One for All again, hopping back to Uraraka and Jiro. 


	2. Meeting the 99 Caverns' Saviors

**Summary for the Chapter:**

> Quick run-down.

**Notes for the Chapter:**

> woooooooooooooooooooooooooooooooooooooooooooooooooooooo

Izuku, powering up with ten percent of One for All, jumps back to Uraraka and Jiro’s location, almost getting lost within all the thick foliage. He lands on his feet, breaking his fall with a roll, just to be safe. 

Ochaco runs to him, asking “Did you find anything we can use to help Jiro?” 

He shakes his head. “No, but there’s a place we can take her. It’s unconventional, but it’ll work.” 

“We can take them to this ‘Shane Gang’. I met a native that said they have a ‘healer’ slug.”

“A slug?” Ochaco questioned. 

“Yeah. Uh, where’s the little guy I left with you?” 

“Oh, he’s sitting.. Standing? He’s next to Jiro.” 

Izuku walks over to Jiro’s still battered, yet alive body, gently picking up the slug and placing it on his shoulder. He pets its head with a single finger.

“According to the locals, this is a slug. I’ll uh, have to carry Jiro… Or I can bring them to.. Yeah, that sounds better. So uh, maybe stay here. Again.” 

“Oh, o-okay.” 

Izuku hops off again, going back to his previous location to try and locate the Shane Gang. He stops at the doorway of the unusual house, pressing the button which he presumes to be a doorbell. Sure enough, a faint jingle resounds within the house. 

A surprisingly young male voice calls out from inside. 

“Coming!” 

A few seconds later, the door opens to reveal a young boy. No time to question. Jiro and Ochaco need help. 

“Who and who need help?”

“U-Uh, my friends! They got quite a bit of their bones broken, but they need your… ‘healer slug’? Do you really have one of those?” 

The boy nods. He looks back into the house, and calls for someone or something called ‘Pronto’. What comes out is unexpected.

“Well, next time going to interrupt my meal of a delicious broiled Cavern Crawler, I’m going to deface your Mecha-Beast!” 

It’s a sort of Spanish accent, and this.. humanoid mole comes out. He’s half of this boy’s size, yet he assumes from the facial hair and that he’s more than twice his age.

“What. What- what is this? Why have you brought me out here to look at a child in a strange costume? Go away, we are not participating in Cavern Spooks. It’s not even October!” 

“Pronto, he needs help with his friends, and I need backup. Trixie is out, Junjie is meditating, and Kord is… Actually, what  _ is _ Kord doing?”

“He said he needed more mechanical supplies.” 

“That. Anyways, yeah, sure! I’ll help your friends out.” The boy calls for ‘Doc’, and a green, cycloptic slug hops out of his backpack and onto his shoulder. 

“Take us to ‘em.” 

“Uh, okay! Try to keep up, please!” 

They get on these mechanical animals, and he activates five percent of One for All. He sprints off, and they follow behind him.

Soon, they arrive at the clearing in which Uraraka and Jiro are staying, and Jiro’s condition seems to have worsened. The boy gets off his vehicle, and kneels down next to Jiro. He nods to the green slug on his shoulder, and unholsters his gun. The slug hops in the barrel.

His eyes widen in shock. “Wait, no, don’t sh-”

The gun fires, and Izuku activates One for All, jumping at the boy and revving up a punch. The slug comes out in a different form and latches onto the ground, near both Jiro and Uraraka, and he was also slowly gaining distance on the slug. It lets out a blinding green blast of energy, and he has to close his eyes. 

[|-----|]

When he opens his eyes, the verdant greenery pops out more and seems more vibrant than before, flowers blooming on the grass right before his eyes. He turns to look at Jiro and Uraraka, who have their wounds healed. They look down at their hands in awe, and Jiro jumps up, apparently feeling more energized than ever. 

The boy. Where was he? Izuku looks to his left, and sees the boy holstering his gun. He kneels down with an open-faced palm, and the slug hops onto his hand. He lifts it up to his shoulder and it hops within the sling bag on his back. 

“Well, there you go! Should be all healed up.”

Jiro clenches her fists, throwing a few light punches, then proceeds to do a few leg stretches. “Wow. It feels a lot better, holy shit.” 

Uraraka rolls her shoulder, moving her forearm a bit too. Completely healed up, down to the last skin cell. “Yeah, it’s all better, and I feel really refreshed, too!” 

Izuku feels himself up a bit. His ribs aren’t broken anymore. How? Well, obviously the slug, but there has to be some sort of biological explanation to this. The immense blast obviously had powerful effects, but it held no force behind it. It was akin to a warm blanket of sun rays enveloping his body, and the sensation that coursed through his body refreshed and energized him, bringing him back to full strength. 

“Amazing..” Was all he could mutter out, looking at his hands. 

Once the sensation faded, the contrast of the warmth compared to the mud on his costume brought him back to Earth, reminding him to get changed. 

“Hey, uh.. You know where we can get new clothes?” 

“Actually, yeah! There are a lot of stores giving out their old and out-of-fashion clothing, and I’m pretty sure we have some extra bandolieeeeeerss…” The boy trails off, suddenly staring at the slug on his shoulder. 

“Oh.  _ Oh my god.  _ Is that a Jadeite Slicksilver?” The boy seems to know a lot about the various types of slugs. From his reaction, the one on his shoulder was apparently a rare type of an already existing slug. 

“Oh,  _ that’s _ his species? That’s actually a cool name.” 

He reaches his finger up and gently scratches the Slicksilver’s head, the slug chirping at the affectionate action. He reaches into his pocket. Only a few thousand yen.

“Is there a way to convert money in this place?”

“Actually, yeah. Multiple methods, a lot of which I don’t advise.”

“What are the ones you  _ do _ advise?” 

“There’s always the contracts, slug-slinging competitions, and mecha-beast races.”

“All things that my mother advised against. And yet, here I am. About to gamble my life for currency.” He sighs. “Well, no time to waste. Also, if possible, could we stay at your place?” 

“Sure! We have one guest room, and extra sleeping bags and pillows. But I think you guys will have to get some new clothes and a shower first, you guys stink. No offense.” 

“None taken. Is there a slug-slinging competition going on nearby?”

“Yeah, actually. There’s a tourney going on and I think it’s about to start, so we better hurry!” 

“Well, let’s get going, then.” 

“Oh- before I go, do you uh… know how to sling a slug?”

“Nnope.”

The boy sighs. “Well, introductions first. I’m Eli Shane, and this is Pronto Geronimole. We’re two of the five members of the Shane Gang. And you guys are?”

Izuku gets up and offers a hand to shake. “I’m Izuku Midoriya, and these are my two friends Ochaco Uraraka and Kyoka Jiro.”

Eli smiles, taking Izuku’s hand and giving it a shake. 

“Welcome to the 99 Caverns, guys. Enjoy your stay.” 


	3. Protoforms, Velocimorphs, and Megamorphs

**Summary for the Chapter:**

> Izuku gets a little lesson from Eli.

**Notes for the Chapter:**

> back with another chapter within a week lets go

“The 99 Caverns, huh?”

“Yeah, it’s a pretty large place to live in. Some areas are scalding hot or freezing cold, but they all make up environments for the slugs and the people to live in.”

As they walk through a variety of mushroom forests, large trees, and various fauna, Izuku and his classmates can’t help but be mesmerized by the cavern’s environment. It looks like something straight out of a fever dream. He takes off his glove, gently placing a hand on a mushroom cap. It’s damp, like it had been freshly rained on. He lifts his hand, gazing upon the print that he’d left on the mushroom.

“This world is pretty, right?”

He turns to Eli, who had a sort of assuring smile on his face. He nods, giving a smile of his own.

“Definitely.”

[|-----|]

“Alright, barebones of slug-slinging! First, you need a blaster.”

Eli taps the strange contraption on his left wrist, and then pats the blaster on his side.

“These are both blasters. The one on my wrist, of course is a wrist blaster, but this one’s a traditional blaster. Shoot it like any other gun. Pull the trigger, and bam, out goes the Velocimorph.”

A question immediately comes to mind. Izuku raises his hand, and Eli stops what he’s doing.

“What’s a Velocimorph?”

“Wh- Oh, right. Forgot you weren’t from here. Okay so- a Velocimorph is basically the form that a slug reaches when they reach a speed of one hundred miles an hour. All slugs have ‘em… except Floppers.”

“Floppers?”

“Yeah, Floppers. They don’t have a Velocimorph, but they’re as useful as any slug, if you’re crafty enough.”

A small slug hops out of Eli’s backpack. Its antennas are flopped over its eyes, and said eyes have eyebags. It sports a dull yellow-ish white, with an accent of murky green spots on both eyes and a spot on their belly. It looks depressed, honestly.

“And then you got Megamorphs!”

“Megamorphs,” Izuku parrots.

“Yep.” Eli points to the sort of cog-like attachment on the central part of his traditional blaster. He then smirks.

“This is an Accelerator. Attach it to the core of your blaster, and you’re basically guaranteed a Megamorph. Oh- and Megamorphs only happen when your slug reaches a speed of one thousand miles per hour. They’re amped up forms of the Velocimorphs, and once a slug experiences a Megamorph, it changes their Protoform! Hey, Burpy, come on out.”

Yet another slug hops out of Eli’s backpack. Orange is the first color Izuku notices, along with fiery accents. It chirps in confusion at Eli, to which he responds: “Listen, we got some new people! We gotta show ‘em your Megamorph, Burpy!”

Chirping happily, ‘Burpy’ lets a grin creep its way onto its face. It hops onto the brim of Eli’s Blaster, fitting firmly into the blue canister that rested in the hollow area of the Blaster.

Eli grins as well, clenching his fist onto the handle that the Blaster provided. Suddenly, a whirring sound cuts its way through the serene silence of the forest. Slowly, but consistently, the cog-like device begins to spin and light up. Soon, the whirring begins to pick up, both in pitch and volume. Eli braces himself, placing a hand on the Blaster to presumably secure its position. Digging his feet into the green grass beneath him, he pulls the trigger.

And once again, that laser-like sound rung through his ears, clearly imprinting the soundwave in his ears. The noise was so immense that he could feel it resonate within his ribcage, like he felt the full force of a sperm whale’s echolocation, clearly grasping where his heart and organs were.

Out shot Burpy from the barrel of the gun, who rotated 360 degrees, turning into a larger version. Like a more… muscular? Like a thicker bat, but.. flaming! Flaming and immensely mesmerizing! Burpy did a loop-de-loop, leaving a ring of fire, then it returns to its Protoform and lands perfectly on Eli’s shoulder.

“… Wow,” Izuku gasps.

He was breathless. That was exhilarating. No words were found. All he could do was break down in a muttering spree, reaching for the notebook and pen he kept in his back pocket. He immediately began taking notes about the new phenomenon. Well, of course there had to be more types of slugs, right? And they all had different purposes, appearances, etcetera!

This was like Quirks, but he might be able to closely analyze them without being too creepy about it! … Maybe he still had issues.

“Man, you probably do have issues.”

“I- What? W-Was I muttering?”

“Yep. You got a knack for studying?”

“Y-Yes. I like analyzing things that I find interesting, like Quirks and now slugs!”

“Quirks?”

“Y-Yeah. You know, I can do this?”

Izuku stands up, pocketing the pen and notebook. Tapping into the depths of One For All, bright red streaks of energy appear on his face and body, enveloping his body in some sort of warmth. He brings out the measly eight percent of its power, exhaling deeply to concentrate. Eventually, he’s surrounded by the ever-so-familiar green arcs of lightning that crackle around his body every now and then.

“Whoaaa! That was so cool!”

Izuku chuckles awkwardly at Eli’s excitedness. He was still getting a hang of how to handle compliments properly.

“So uh, _my_ Quirk gives me all-around strength, which I can just access. But if I use too much of it, I break my bones. Can’t handle the power yet, hah.”

“Yikes. Did you actually ever break your bones?”

“Oh yeah, yeah, definitely. Pretty sure I wasted both of my arms fighting a classmate of mine in a festival.”

“A _festival?_”

“Well- It’s more like a big sports event.”

“You broke your arms for sport.”

“Yyyyes?”

“Damn. You’re all better now, though, right?”

“Definitely. I can move like a well-oiled machine now.”

“Well, if you gotta break your arms again, you got me and Doc to help you out.”

Izuku smiles. It’s nice. He’s nice.

[|-----|]

Kyoka lays on the couch, upside down, next to Ochaco. Apparently Izuku was out doing something with slugs, or something. She adjusts herself right side up, since she was getting awfully dizzy.

“Say, whaddya think Midoriya’s doing?”

No answer. She turns to see Ochaco blanking out, staring at nothing in particular. She seems down about something. Kyoka scoots closer, waving her hand in front of Ochaco, who reels back in slight surprise.

“Yo, Gravity Girl.”

“W-What is it?”

“You blanked out. You okay?”

“Mmh… I guess. Just thinking about our situation.”

“What about it?”

“Well- we’re essentially trapped down here. We don’t know the norm, people have really powerful guns, apparently they use animals as ammunition, and it just looks like a bunch of forest! It doesn’t look anything like Musutafu or U.A.!”

“Well, if you put it like that, we’re kinda fucked, aren’t we?”

“Fucked… Yeah.”

The door opens, and they both see Eli and Midoriya walking in, happily conversing with each other about slugs.

“Oh- Hey, Midoriya.”

“H-Hi, Deku.”

“Hey! So, apparently, slugs are really useful? I think we can just fight them though.”

Eli seems taken aback. “Fighting slugs? What?”

“You saw what my Quirk can do. I could probably knock out a slug from mid-air if I got the timing right.”

“Oh.. yeah. Speaking of Quirks, what’re your friends’ Quirks?”

[|-----|]

“Oh- uhm. Jiro here has extendable earlobes, and the edges of her earlobes are shaped like headphone jacks. She can pump her heartbeat through whatever she sticks the jacks into at a really loud volume. Like, almost earthquake-causing volume.”

Kyoka salutes with two fingers, allowing her jacks to point at Eli.

“And my friend Uraraka has a gravity Quirk. If she touches anything with all five of her fingers, she can remove their gravity. Her maximum weight removal is five tons, though.”

“Wow.. All really useful. Kinda makes me wish I had a Quirk, heh.”

Izuku recoils slightly. He forgets they’re Quirkless. As he was once a Quirkless, it wasn’t a very desirable experience that he ever wishes to go through again. Bullies on every corner, stared at like a weird lab experiment, shunned from the rest of society, save for his family. Maybe if his family hadn’t cared so much, they would’ve shunned him too.

He shivers at the thought. Now’s not the time to reminisce.

“So, we sleep out here, for now?”

“Unfortunately, yeah. Until you can get some actual living space, and some currency, you’ll have to sleep on the couches. They’re kinda stiff, so don’t expect to get too comfortable.”

Izuku hops onto one of the seats, between the spaces Jiro and Uraraka sit. He gets shivers up his spine from the impact.

“Wow, you’re right.. That isn’t very soft.”

Eli chuckles. “Well, Trixie and I can teach your friends about slugs and the Caverns tomorrow, if they want.”

“Yeah, that’d be great,” Uraraka pipes up.

“Meh… Not too keen about handling bugs.”

“They’re not bugs. And they’re fine as pets too! A healthy slug is a happy slug.”

“I’ll think over it. I’m not changing my mind though; I refuse to touch one of those. I hate slimy things.”

“Fine, fine.”

Two more people enter through the door, a redheaded girl and a really big blue dude with an abnormally large upper body. His legs probably took up a third of his torso.

“Ah, so these are the new kids,” the blue dude speaks up.

Eli approaches the blue guy, doing some sort of handshake with him.

“Yep! They’ve got some cool stuff to show you tomorrow once we get some R&R and get properly rested.”

The girl speaks up. “Oh, and they’ve got some nice tech on ‘em too. Maybe we can use that if they let us.”

“Right, right. Well, it’s getting late. Go take a shower, you two smell of cavern crawlers.”

The Molenoid yells from the kitchen. “Well, I’ll have you know that cavern crawlers are delicious!”

Eli chuckles. “Well, now that that’s said and done, I can confidently say that you guys might fit in well here. Everyone in the Shane Gang’s fairly friendly, so just ask around and I’m sure you’ll get to know some people well!”

Izuku looks to Jiro, then Ochaco, then back at the trio in front of them.

“Thanks for having us.”


End file.
